1. Field of the Invention
The present invention relates to a method and an apparatus for detecting electrically-conductive material (hereinafter simply referred to as "conductive material") contained in glass fiber in a state of maldistribution, and relates to a method and an apparatus in which existence of fine conductive material which is possibly contained in glass fiber can be detected easily and accurately in the condition that the glass fiber is running in a manufacturing process of the glass fiber.
2. Description of the Related Art
Fine particles of conductive material may sometimes be contained in a state of maldistribution in glass fiber such as glass filaments, glass yarns or strands, or the like, constituting glass roving or glass cloth. This is because glass may contain metal components due to batch material, clay brick, or the like. The conductive material contained in glass fiber may cause a problem that electrical insulating properties are deteriorated when the glass fiber is applied to printed circuit substrates or the like. Accordingly, it is necessary to remove such a part of the glass fiber in which conductive material is contained, in the manufacturing process of the glass fiber.
As methods of detecting conductive material contained by a very small amount in glass fiber, conventionally known are a method which utilizes changes in dielectric constant, a method which utilizes a phase difference in a microwave, and a method which utilizes electric discharge. In the detection method utilizing changes in dielectric constant, it is necessary to directly measure the dielectric constant of glass fiber. In the detection method utilizing a phase difference in a microwave, conductive material or a fault in glass fiber is detected by a phase difference between a transmitting waveform and a receiving waveform of a microwave (JP-A No. 60-20138). In the detection method utilizing electric discharge, conductive material contained in glass fiber is detected by causing high-frequency discharge on the conductive material (JP-A No. 59-214748).
In the detection method utilizing changes in dielectric constant, there is such a problem that when the amount of conductive material contained in glass fiber is extremely small, the value of a dielectric constant to be measured is so small that a measuring instrument becomes insufficient to indicate the value of a measured dielectric constant so that measurement becomes impossible. Unless glass fiber is in a stationary state, generally, it is impossible to measure a dielectric constant, and therefore the detection method utilizing changes in dielectric constant cannot be applied to the case where glass fiber is moving. Accordingly, there is a problem that this method cannot be utilized at all in production management of glass fiber. In the detection method utilizing a phase difference in a microwave as well as in the detection method utilizing electric discharge, there is a disadvantage that the capability of detecting conductive material contained in glass fiber may be extremely lowered owing to an influence of a hiding action of moisture, size, dust, or the like, attached on the surfaces of the glass fiber. Granting that there is not such a hiding action due to those factors, among various kinds of conductive material contained in glass fiber, it has been impossible to detect those smaller than 2 mm in length in the axial direction of the glass fiber as a matter of fact.